Spherical RNA plant viruses are excellent model systems for studying protein-protein and protein-RNA interactions. Tomato Bushy Stunt Virus (TBSV) is an excellent system for study because x-ray diffraction studies have provided a three dimensional structure of the icosahedral portion of the virus at 2.9A resolution. We are determining the amino acid sequence of the 40,000 dalton TBSV goat protein, and are studying a minor 86,000 dalton protein which is present in one copy per TBSV virion. We are also probing which amino acids of the coat protein interact with the viral RNA by studies which covalently crosslink the viral RNA to the coat protein. TBSV also provides a model system in which to examine assembly and disassembly of macromolecular complexes, and to identify the structural and chemical basis for control of assembly specificity and disassembly timing. Toward this end, we will attempt in vitro reconstitution experiments using purified TBSV coat protein, minor protein, and RNA.